President Donald Trump tweeted Tuesday night about Chicago’s violence, saying he will “send in the Feds!” if the city “doesn’t fix the horrible ‘carnage’ going on.”

Trump’s tweet refers back to a line in his inaugural address Friday about “the crime, and the gangs, and the drugs that have stolen too many lives and robbed our country of so much unrealized potential. This American carnage stops right here and stops right now.”

The tweet cited numbers — “228 shootings in 2017 with 42 killings (up 24% from 2016)” — that come from Chicago Tribune data used in a news story Monday about violence in the city so far this year. As of Tuesday evening, there had been at least 247 people shot in Chicago, with at least 44 people killed, according to Tribune data.

Chicago Police Department statistics for the month are lower because they do not include shootings on area expressways, police-involved shootings, homicides in which a person was killed in self-defense, or pending death investigations.

A spokesman for Mayor Rahm Emanuel referred reporters to an interview on WTTW-Ch. 11 Tuesday night.

Asked in that conversation about the White House website under the Trump administration citing violence in Chicago, Emanuel said that federal agencies including the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives already do help the city, but more could be done.

“There’s a lot the federal government can do,” Emanuel said, citing gun control, use of federal resources to track illegal guns and federal prosecutions. “And also, fundamentally, in my view, also help fund additional police officers.

“Over the years the federal government’s stepped back their resources, which we have stepped up. The federal government can be a partner, and to be honest they haven’t been for decades.”

In a statement, Chicago Police Superintendent Eddie Johnson said that "the Chicago Police Department is more than willing to work with the federal government to build on our partnerships with DOJ, FBI, DEA and ATF and boost federal prosecution rates for gun crimes in Chicago."

In August, candidate Trump said “very top police” in Chicago had told him the city’s crime problem could be stopped in a week with tougher tactics.

The comment came in an interview with Fox News host Bill O'Reilly, who had asked him how Chicago’s violence could be quelled.

"How?” said Trump. “By being very much tougher than they are right now. They're right now not tough. I could tell you this very long and quite boring story. But when I was in Chicago, I got to meet a couple of very top police. I said, 'How do you stop this? How do you stop this? If you were put in charge — to a specific person — do you think you could stop it?' He said, 'Mr. Trump, I'd be able to stop it in one week.' And I believed him 100 percent.”

At the time, Chicago police said Trump had not met with top brass since at least March. The Trump campaign did not identify who had claimed to have a one-week solution. "Mr. Trump spoke with some talented and dedicated police officers on a prior visit," Trump spokeswoman Hope Hicks had said in an email.

During the campaign, Trump often cited Chicago violence as an example of rampant urban crime that would be addressed if he were elected.

In September, Trump suggested in a TV interview that Chicago “is out of control” and needed to employ controversial “stop-and-frisk” police practices to stem violence.

“We did it in New York, it worked incredibly well,” Trump said about stop-and-frisk practices. "You understand, you have to have, in my opinion, I see what’s going on here, I see what’s going on in Chicago, I think stop-and-frisk. In New York City, it was so incredible, the way it worked. Now, we had a very good mayor, but New York City was incredible, the way that worked, so I think that could be one step you could do.

“I think Chicago needs stop-and-frisk. Now, people can criticize me for that or people can say whatever they want."

In Chicago, police had used a similar practice for years, stopping people they deem suspicious and questioning them, sometimes patting them down. In 2015, the American Civil Liberties Union of Illinois considered suing the Chicago Police Department over the excessive use of the practice, which has been condemned by the ACLU as racial profiling.

Chicago police denied racial profiling, but entered into an agreement with the ACLU that required officers to more thoroughly document their street stops. The changes were also incorporated in a new state law.

The complete Trump tweet on Tuesday was: “If Chicago doesn't fix the horrible 'carnage' going on, 228 shootings in 2017 with 42 killings (up 24% from 2016), I will send in the Feds!”

Trump’s tweet came a day after Emanuel made comments critical of the new president. The mayor criticized Trump for focusing on the size of the crowd at his inauguration ceremony and suggested his inaugural speech wasted an opportunity to appeal to “our better angels as a country.”

The mayor also responded to the pro-law enforcement message on whitehouse.gov reading, “The dangerous anti-police atmosphere in America is wrong. The Trump administration will end it.”

Emanuel said police need to have professional standards and public support, and acknowledged the “Ferguson effect” in which some officers may patrol less aggressively to avoid having their actions second-guessed. But Emanuel saw no need for departments to enact tactics like stop-and-frisk.

“Clearly police — there was a reaction of what happened across the country,” Emanuel said. “On the other hand, the choice isn’t just ‘Go back to stop-and-frisk.’ And this is not a bipolar, two camps. We need our police to have high professional standards, the training to support them in those high professional standards and the certainty to be proactively involved.”

While Trump did not say what he meant by the "feds," here's a look at some of the options that might be available:

• NATIONAL GUARD

The most direct — and most extreme — intervention would be sending National Guard troops into Chicago to try and tamp the violence. Both the U.S. president and the Illinois governor have the authority to mobilize the Illinois National Guard. But a federal statute, known as the Posse Comitatus Act of 1878, prohibits the deployment of federal troops in civil law enforcement. While a president could try to find legal loopholes to get around that prohibition, the legalities of any such deployment would pose major obstacles. A heavy-handed intervention could upset many conservatives who advocate for states' rights.Trump has not broached the possibility of using troops, although the idea comes up from time to time in Illinois. When someone asked Illinois Gov. Bruce Rauner about the possibility in August, he ruled it out. He said he had discussed the idea with police, community leaders and the National Guard and that "no thoughtful leader thinks that's a good idea or (that it would) would really provide a solution."

• U.S. ATTORNEY

Current U.S. Attorney Zachary Fardon came under pressure when selected to be the top federal law enforcement official in Chicago three years ago to put violent crime at the top of the city's agenda. But from the start of his tenure, he tempered expectations about what a U.S. attorney's office could do. He had said repeatedly that communities couldn't arrest their way out of the problem of violence and that a more holistic approach — one that also addresses socio-economic problems — is required.

Fardon said in a September speech that his office and federal agencies including the FBI, DEA and Bureau of Alcohol, Tobacco, Firearms and Explosives "have ramped up their resources to help tamp down this spike in violence." He also said federal agencies had launched new crime-fighting programs with city and state officials, though he didn't provide details. "Suffice it to say, all oars from those agencies, including the FBI, are in the water right now," Fardon said.

• GUN CHARGES

Then-U.S. Attorney General Eric Holder promised in 2014 that the Department of Justice would do what it could to fight gun violence in Chicago. That was easier said than done. A records review by the Chicago Sun-Times found numbers of federal gun cases out of Chicago declined from 2012 to 2015. It started trending back up in 2015, with 84 defendants charged under U.S. gun statutes from mid-2015 and mid-2016. Responding to the Sun-Times, Fardon wrote in October that the drop-off in gun charges in 2014 to less than 60 had at least something to do with a federal hiring freeze, when his office went from 172 prosecutors to below 130. The numbers are getting back up to where they need to be, he said. He said half of his prosecutors are focused on the types of cases linked to street-level violence.

• GANGS

Going back decades, a cornerstone of anti-violence measures by U.S. attorneys in Chicago has been to convict and imprison gang leaders. Federal prosecutors in Chicago have used racketeering and gun laws to go after gangs, who police blame for much of the deadly violence. One of the largest street-gang cases in recent Chicago history wrapped up this month, with jurors convicting the core leadership of the notorious Hobos street gang on trial for an alleged racketeering conspiracy that prosecutors say included at least nine killings. But many gang experts point to an unintended consequence of prosecuting gang leaders: Breaking up a gang's command structure can often lead to more inter-gang rivalry and, therefore, to even more violence

The Chicago Tribune's Jeremy Gorner and John Byrne, and the Associated Press, contributed.